This invention relates to a laser beam scanning device adapted for use in, for instance, a laser beam printer in which printing is performed by transferring and setting the information formed by means of a laser beam on a photosensing drum and onto transfer paper.
In the above laser beam, which is printer, the laser beam responsive to information to be recorded, scans the electrified circumferential surface of a photosensing drum in the axial direction of the drum (horizontal scanning), while also scanning it in its circumferential direction upon its rotation (vertical scanning). The latent image thus formed on the circumference of the photosensing drum by virtue of varying electrostatic effects due to exposure to the laser beam is electrophotographically developed on the transfer paper with toners.
The laser beam scanning device typically comprises a semiconductor laser radiating a laser beam responsive to an input signal, and a series of optical elements through which the beam from the laser is conducted to the photosensitive drum, the series of optical elements includes a collimator lens, a cylindrical lens, a polygonal scanner, and a f.theta. lens. In conventional laser printers, these optical elements have been independently mounted on a chassis or assembly base.
Extraordinary precision, which is incomparable to that for other structural parts, is required for setting up the relative distances and relative installation angles between such optical elements, especially between the semiconductor laser, the cylindrical lens, the polygonal scanner and the f.theta. lens. It means that these individual elements must be installed with such high precision. Not only that, the chassis or assembly base for supporting these elements must be manufactured with such extreme precision.
When any failure occurs in the installation precision required for such optical elements due to ambient temperature variations and vibrations, it is necessary to perform part replacement in specially equipped places, as well as re-adjustment with the same precision as in the first assembly. The associated problem have therefore been a resultant time-consuming and less efficient process for production, replacement and adjustment.